[Lynch Syndrome Caused by Germline Alteration of MLH1 in a Young Patient Who Developed Colon and Endometrial Cancer - A Case Report].

A 39-year-old woman underwent right colectomy for type-3 transverse colon cancer, which was histologically identified as well-differentiated stage II A adenocarcinoma with a mucinous component and tumor-infiltrating lymphocytes. The patient was suspected of having Lynch syndrome(LS)since she fulfilled 2 of the revised Bethesda criteria, even though there was no family history of LS. Twelve months after colectomy, abdominal CT revealed thickening of the uterine endometrium. Histopathological examination of biopsy specimens revealed well-differentiated endometrioid carcinoma. Extended hysterectomy with bilateral oophorectomy was performed. Histological examination of the resected specimen revealed well-differentiated endometrioid carcinoma of stage I . Immunohistochemistry analysis of mismatch repair proteins demonstrated loss of MLH1/ PMS2 expression in the colon cancer, but normal expression in the uterine cancer. Genetic testing identified duplication of exons 10-15 of the MLH1 gene, leading to a definitive diagnosis of LS. The patient has not shown any evidence of recurrence or new LS-associated tumors in the 12 years since the last surgery. There is an ongoing debate regarding the pathogenesis of endometrioid cancer, and this case emphasizes the importance of surveillance for gynecological malignancies after colon cancer surgery in female LS patients.